I think Spearow/Fearow should also be an option on this list - Spearow are available in Kanto just one route after Pidgey so I've always considered them
both to be the starter birds of Kanto. Plus, they're in the
very first episode of the anime. Not that I would have chosen Spearow, I just think they deserve a mention
Anyway, Pidgey is my definite choice. Even aside from it being the original which gets my nostalgic gears turning and sends me on a trip down Memory Wharfage, I think it has by far the best design of them all. They've simply yet to come up with cooler looking birds since the Pidgey line. Pidgey itself is obviously nothing special, but Pidgeotto is nothing short of beautiful and they've yet to trump the majestic look of Pidgeot. I don't think they ever will. Simply beautiful feat of animation.
My least favourite is by far the Pidove line. Unfezant is the dorkiest bird I've ever seen in my entire life. And this is a world that includes a two-headed ostrich.